Mechanisms by which cyclodextrins modify drug release from polymeric drug delivery systems

Cross-linked beta-cyclodextrin microcapsules. II. Retarding effect on drug release through semi-permeable membranes

Microcapsules were prepared by interfacial cross-linking of beta-cyclodextrins (beta-CD) with terephthaloylchloride (TC) as described previously. Complexation assays were conducted with propranolol HCl. After 1 h incubation of 50 mg lyophilized microcapsules in 10 ml propranolol solution, the amounts of fixed drug were 507.5+/-8.6 micromol and 811.2+/-16.0 micromol per g lyophilized microcapsules with 1 mM and 2 mM solutions, respectively. A dialysis experiment was then performed. After 1 h incubation of microcapsules (10 or 50 mg) in 10 ml of 2 mM propranolol solution, the suspension was dialysed against a phosphate buffer pH 7.4 at 37 degrees C. The drug diffusion was all the more retarded that the amount of added beta-CD microcapsules was higher. Finally, double microcapsules were prepared using a suspension of beta-CD microcapsules (10-100 mg) in a solution of methylene blue in an acetate buffer pH 7.4. After adding human serum albumin (HSA), the suspension was emulsified in cyclohexane and double microcapsules were obtained by cross-linking the HSA with TC. In vitro release studies showed that the incorporation of beta-CD microcapsules resulted in a decrease in release rate of methylene blue, the decrease being related to the amount of encapsulated beta-CD microcapsules. The study then suggests interesting applications of beta-CD microcapsules for modulating the release rate of drugs through semi-permeable membranes.

Influence of betacyclodextrin on the release of poorly soluble drugs from inert and hydrophilic heterogeneous polymeric matrices

The release behavior of poorly soluble drugs (naproxen and ketoprofen) from inert (acrylic resins) and hydrophilic swellable (high-viscosity hydroxypropylmethylcellulose) tableted matrices containing betacyclodextrin (betaCD) was investigated. The results demonstrated that, in both cases, betaCD can enhance the rate of drug release. Matrices obtained from formulations in which lactose replaced betaCD were also evaluated. BetaCD in inert matrices causes a dramatic increase in the rate of drug release, higher than that promoted by lactose which merely acts as a channelling agent. This result suggests that possible in situ formation of the drug-betaCD complex. which causes an improvement in apparent drug solubility, could have a greater influence on the rate of drug release than the possible increase of water uptake by a soluble filler. Indeed, if the opposite were true, lactose would be more effective in increasing the rate of drug release than betaCD, because of its greater solubility in water. On the contrary, in the case of hydrophilic matrices, lactose proves to be much more effective in promoting drug release than betaCD. It seems that, while the bulky interaction compound can freely diffuse through water-filled pores of inert systems, its diffusion through swollen macromolecular chains of hydrophilic matrices may be hindered. This hypothesis was supported by data obtained from binary (drug/polymer) and ternary (drug/polymer/betaCD) hydrophilic matrices using a betaCD-containing dissolution media.

Combined hydroxypropyl-beta-cyclodextrin and poly(alkylcyanoacrylate) nanoparticles intended for oral administration of saquinavir

The aim of this study was to prepare and characterize an hydroxypropyl-beta-cyclodextrin-saquinavir inclusion complex with the purpose of incorporating this complex into poly(alkylcyanoacrylate) nanoparticles in order to increase the drug loading. Hydroxypropyl-beta-cyclodextrin-saquinavir complex was characterized by thermal (differential scanning calorimetry), crystallographic (X-ray diffractography) and spectroscopic methods (circular dichroism, H1-NMR). Nanoparticles were prepared by polymerization of alkylcyanoacrylate monomers (isobutyl- and isohexylcyanoacrylate) in a water solution of the complex and further characterized. The apparent solubility of saquinavir was increased 400-fold at pH 7.0 in presence of hydroxypropyl-beta-cyclodextrin owing to the formation of a drug-cyclodextrin complex as demonstrated mainly by 1H NMR and confirmed by other techniques. Saquinavir-loaded nanoparticles could be easily prepared in the presence of a drug-cyclodextrin complex. It was found that large amounts of cyclodextrins remained associated with the particles, resulting in a 20-fold increase in saquinavir loading compared to nanoparticles prepared in the absence of cyclodextrins. This study has shown that the loading in saquinavir of poly(alkylcyanoacrylate) nanospheres could be dramatically improved by simultaneously increasing the apparent solubility of the drug in the preparation medium and the amount of cyclodextrin associated with the particles, making these nanospheres a promising system for oral application.

Modulation of drug release from hydrogels by using cyclodextrins: the case of nicardipine/beta-cyclodextrin system in crosslinked polyethylenglycol

A simple approach is presented to modulate drug delivery from swellable systems by using complexants. The effect of complexants has been interpreted by means of simple mass balances on diffusing species and the involved relevant parameters have been individuated. The application of this strategy to the release of nicardipine (NIC) from swellable systems by using beta-cyclodextrin (CD) as complexant has evidenced the potential of the approach to tailor drug release. Crosslinked polyethyleneglycol has been synthesized, characterized and used as the swellable matrix. Swelling kinetics, NIC and CD diffusivities in the swollen matrix and NIC/CD phase solubility studies have been performed. The polymer matrix has been loaded with pure NIC or with NIC and CD at different ratios and release kinetics evaluated. Release profiles have shown that the presence of CD significantly affected drug delivery by decreasing the effective diffusivity of NIC. The higher the CD/NIC ratio the slower is the release. This effect has been interpreted on the basis of the proposed model and physically sound assumptions.

Substituted beta-cyclodextrins interact with PAMAM dendrimer-DNA complexes and modify transfection efficiency

The efficiency of PAMAM dendrimer-mediated DNA transfer can be improved by the addition of substituted beta-cyclodextrins (beta-CDs) as formulation excipients. In vitro CAT expression increased approximately 200-fold when dendrimer/DNA/beta-CD formulations were applied on the surface of collagen membranes. The inclusion of beta-CD into the formulations resulted in particles that were smaller and more evenly distributed on the surface of the solid support. The average size of the complex formed at 50 microg/ml and at charge ratio of 1 decreased from 156 nm to 5.8 nm and 21.2 nm in 0.025-0.1% w/vol beta-CDs. Sulfonated beta-CDs bind to dendrimer and in the increased concentration may displace DNA in the dendrimer/DNA complex. High concentrations of amphoteric beta-CD do not dissociate dendrimer/DNA complexes; however, they may decrease their ability to transfect cells. At the optimized formulations the surface-modified beta-CDs may enhance solid support-based transfection in vitro, through modification of dendrimer/DNA complex composition and improved surface distribution.